Use Script Host before PowerShell for Windows parent query fallback

lib/overcommit/utils.rb

@@ -293,7 +293,29 @@ def windows_parent_command
         native_windows_parent_command
       rescue LoadError, StandardError
         # win32ole is optional and absent from newer Ruby distributions.
-        # Fall back when it is unavailable or the COM query is denied.
+        # Use Script Host when it is unavailable or the COM query is denied.
+        scripted_windows_parent_command
+      end
+
+      def scripted_windows_parent_command
+        begin
+          result = execute([
+            'cscript.exe', '//nologo', '//B', '//U',
+            File.expand_path('../../libexec/overcommit-parent-command.js', __dir__),
+            Process.ppid.to_s,
+          ])
+          if result.success?
+            command = result.stdout.dup.force_encoding('UTF-16LE').encode('UTF-8').
+              delete_prefix("\uFEFF").strip
+            return command.empty? ? nil : command
+          end
+        rescue Errno::ENOENT, ChildProcess::LaunchError, EncodingError
+          # Preserve PowerShell when Script Host is disabled or unavailable.
+        end
+        powershell_windows_parent_command
+      end
+
+      def powershell_windows_parent_command
         result = execute([
           'powershell.exe', '-NoProfile', '-NonInteractive', '-Command',
           "(Get-CimInstance Win32_Process -Filter 'ProcessId = #{Process.ppid}').CommandLine",

libexec/overcommit-parent-command.js

@@ -0,0 +1,11 @@
+// Query the same WMI property as PowerShell without its startup overhead.
+// cscript //U writes redirected output as UTF-16LE.
+var pid = String(WScript.Arguments(0));
+if (!/^\d+$/.test(pid)) WScript.Quit(2);
+var service = GetObject('winmgmts:root/cimv2');
+var processes = service.ExecQuery('SELECT CommandLine FROM Win32_Process WHERE ProcessId = ' + pid);
+var items = new Enumerator(processes);
+for (; !items.atEnd(); items.moveNext()) {
+  var command = items.item().CommandLine;
+  if (command !== null) WScript.StdOut.WriteLine(command);
+}

spec/overcommit/utils_spec.rb

@@ -219,6 +219,72 @@
       end
     end
 
+    context 'when Windows falls back to Script Host' do
+      let(:command) { 'git -C "C:/Users/José/项目" commit --amend' }
+      let(:output) { "\uFEFF#{command}\r\n".encode('UTF-16LE') }
+      let(:script_result) { Overcommit::Subprocess::Result.new(0, output, '') }
+
+      before do
+        Overcommit::OS.stub(:windows?).and_return(true)
+        described_class.stub(:require).with('win32ole').and_raise(LoadError)
+        described_class.stub(:execute).with(array_including('cscript.exe')).
+          and_return(script_result)
+      end
+
+      it 'decodes the complete Unicode command line and removes its BOM' do
+        described_class.should_not_receive(:execute).with(array_including('powershell.exe'))
+        subject.should == command
+      end
+
+      context 'when the process has exited' do
+        let(:output) { '' }
+
+        it 'returns nil without retrying PowerShell' do
+          described_class.should_not_receive(:execute).with(array_including('powershell.exe'))
+          subject.should be_nil
+        end
+      end
+
+      context 'when the script fails' do
+        let(:script_result) { Overcommit::Subprocess::Result.new(1, '', 'Access denied') }
+
+        before do
+          described_class.stub(:execute).with(array_including('powershell.exe')).
+            and_return(Overcommit::Subprocess::Result.new(0, "#{command}\n", ''))
+        end
+
+        it 'falls back to PowerShell' do
+          subject.should == command
+        end
+      end
+
+      context 'when Script Host is unavailable' do
+        before do
+          described_class.stub(:execute).with(array_including('cscript.exe')).
+            and_raise(Errno::ENOENT)
+          described_class.stub(:execute).with(array_including('powershell.exe')).
+            and_return(Overcommit::Subprocess::Result.new(0, "#{command}\n", ''))
+        end
+
+        it 'falls back to PowerShell' do
+          subject.should == command
+        end
+      end
+
+      context 'when Script Host returns invalid Unicode' do
+        let(:output) { "\x00".b }
+
+        before do
+          described_class.stub(:execute).with(array_including('powershell.exe')).
+            and_return(Overcommit::Subprocess::Result.new(0, "#{command}\n", ''))
+        end
+
+        it 'falls back to PowerShell' do
+          subject.should == command
+        end
+      end
+    end
+
     context 'when there is no parent' do
       before do
         Process.stub(:ppid) { 0 }